SHRIMP POPULATION STUDIES 



The question of whether or not more stringent 

 conservation measures would increase shrimp 

 abundance has given rise to controversy among 

 some segments of the shrimp industry. Pro- 

 ponents of restrictive laws contend that over- 

 fishing and, especially, the harvesting of 

 small shrimp have caused a decline in land- 

 ings. On the other hand, fishermen and proc- 

 essors who supply the demand for small shrimp 

 argue against such legislation. Little evidence 

 has been brought forth to date to support 

 either side. This report illustrates that present 

 harvesting practices probably have little real 

 effect on the abundance or long-term welfare 

 of shrimp stocks. 



Concern about shrimp resources becomes 

 especially widespread during years of poor 

 harvests. Concern was great in 1957 and 1961 

 when the Louisiana white shrimp crop failed 

 to live up to expectations, and in 1961 and 

 1962 when catches of brown shrimp were 

 poor from Louisiana and Texas waters. Atten- 

 tion has also focused on the Tortugas pink 

 shrimp grounds off the southwestern coast 

 of Florida where some groups believe the 

 fishery is endangered because fishermen catch 

 too nnany small shrimp. 



Landing data gathered from various shrimp 

 fisheries in the Gulf provide valuable informa- 

 tion that can be used to gain insight into the 

 causes of fluctuations in shrimp abundance. 

 Detailed landing statistics on comnnercial 

 shrimp have been collected for all areas of 

 the Gulf since January 1956. Landing data 

 collected before that time often are not strictly 

 comparable because of variations in collecting 

 and recording practices. An exception may 

 be the landing data from the Tortugas grounds 

 which, fortunately, are available for most 

 of the years since the fishery began in 1950. 

 No marked changes or trends in the annual 

 landings from the Tortugas grounds have oc- 

 curred during this 14-yr. period (fig. 19). 

 Years of better than average or poorer than 

 average harvests are evident, but occur with 

 no particular regularity. Likewise, the sizes 

 of the shrimp landed from the Tortugas grounds 

 have changed little during recent years. (See 

 table 7.) These data indicate that neither 

 intensive fishing nor harvesting small shrimp 

 has had a significant effect on the Tortugas 

 pink shrimp population. The relative stability 

 of this fishery is of particular interest be- 



Table 7. — Comparison of the sizes of pink 

 shrimp landed from the Tortugas grounds 

 luring recent and past years 



cause, with the exception of brief periods, 

 no laws restricting the catch of shrimp have 

 been enforced. 



Landing data on Louisiana white shrimp 

 and Texas brown shrimp (fig. 20) reveal 

 the comparatively brief seasons and marked 

 annual differences in shrimp abundance that 

 characterize these fisheries. In contrast to 

 the Tortugas pink shrimp stock, which is 

 fished heavily for almost 9 mo. of the year, 

 the white and brown shrimp populations sup- 

 port intensive fishing for only a 4- to 6-mo. 

 period. This difference in length of fishing 

 seasons stems from the fact that large num- 

 bers of young pink shrimp move onto the 

 Tortugas grounds twice each year, during the 

 spring and fall, whereas white and brown 

 shrimp stocks are replenished once a year. 

 The year-to-year differences in the abundance 

 and catch of white and brown shrimp are 

 caused by annaul variations in the survival 

 of larval shrimp. Similar variations occur 

 in the survival of young pink shrimp but have 

 less noticeable effects on landings because 

 shrimp from more than one brood are com- 

 monly on the Tortugas grounds at the same 

 time. 



A clue to the type of factors that cause 

 poor survival among larval shrimp has be- 

 come apparent from patterns in landing data. 

 Comparisons of shrinnp catch per unit of 

 fishing effort (pounds per hour) along the 



TORTUGiS PINK SHRIMP 



« I 



Z 



o 



do 



i 



1952 1953 1951 1955 1956 .95' 1958 1959 I960 i96i 1962 |9GJ 1964 



Figure 19. — Monthly landings from the Tortugas pink shrimp fishery, June 1951 to March 1965. 



24 



